Effective breast cancer treatment options are predictable based on the way certain genes act or express themselves, new research shows.

The findings, published in the journal Oncogene, offer proof that gene expression patterns can help direct the type of therapy a patient receives, paving the way for more targeted and personalized approaches to care.

“Breast cancer has numerous subtypes,” says Eran Andrechek, a physiology professor at Michigan State University. “Treatments for these various subtypes have to be different because there are different genes that drive the cancer.”

Estrogen- or progesterone-receptor positive breast cancer, in which hormones drive cancer growth, is one subtype. Other subtypes include human epidermal growth factor receptor 2, or HER2, which is a protein that also promotes the development of the disease.

Another type, triple-negative breast cancer, or TNBC, isn’t driven by either the HER2 protein or hormone receptors and is the one that Andrechek focused on in the study.

For the study, Andrechek and doctoral student Jing-Ru Jhan first examined the unique genetic characteristics and differences within each TNBC tumor. Then they took the genomic information they gathered and compared it to various drugs that could target the specific tumor activity.

“Triple-negative breast cancer is highly aggressive and currently there are limited treatment options,” Andrechek says. “By looking at the particular gene expression patterns of this cancer and determining the pathways that were activated, or turned on, we identified certain drugs that could turn these pathways off and stop tumor growth.”

The findings show that a three-drug combination, including two FDA-approved drugs—Afatinib and Trametinib—also targeted a specific pathway associated with triple-negative breast cancer and together, were effective at stopping the cancer’s growth. Currently, both drugs are commonly used for other types of cancers.

The proof-of-concept study is a positive first step in determining the feasibility of this type of treatment approach, Andrechek says.

“We tested several other drug combinations too and when we expanded our study to include human breast cancers that were grown in mice, we received the same positive result. This gives us a much clearer indication that targeted, individualized breast cancer treatment is viable.”

The National Institutes of Health and the Susan G. Komen Foundation funded the study.